Chemical mechanical polishing (CMP—also referred to as chemical mechanical planarization or chemical mechanical etching) is a well-known technology used in fabricating advanced photonic, microelectromechanical (MEM), and microelectronic devices, such as semiconductor wafers. See e.g. Chemical-Mechanical Processing (Springer Series in Materials Science), Michael R. Oliver, Springer Publ., (Mar. 24, 2006); Microchip Fabrication, Peter Van Zant, McGraw-Hill (2004); Chemical Mechanical Polishing in Silicon Processing, Volume 63 (Semiconductors and Semimetals), Eds. Shin Hwa Li and Robert O. Miller, Academic Press (1999); Chemical Mechanical Planarization of Microelectronic Materials, Steigerwald et al., John Wiley & Sons (1997).
In the field of semiconductor fabrication, chemical mechanical polishing is used to planarize metal and/or oxide substrates. CMP uses both chemical and mechanical action to obtain the desired planarity of the surface to be polished. Chemical action is provided by a mixture of chemicals which is termed as “slurry” usually consisting of abrasives and various additive compounds which include family of chelating agents, passivating agents, oxidizing agents, accelerators etc., Mechanical action is provided by pressing to-be-polished substrate onto the surface of a polishing pad adhered to a moving platen. Movement of platen is typically linear, rotational or orbital. In a typical chemical mechanical polishing process, a rotating wafer holder brings the wafer to be in contact with a polishing pad or CMP pad. One of the key consumables in conventional CMP processes is the CMP pad or polishing pad. The CMP pad is mounted on a rotating platen. A polishing medium, such as an abrasive slurry, is applied between the wafer and the pad.
The invention relates to chemical mechanical planarizing formulation for selectively removing ruthenium metal layers in the presence of interconnect structures of integrated circuit devices. Copper (Cu) is being used as an interconnect metal in the sub-100 nm generation of integrated circuits to enhance operating speed and reliability. Diffusion barriers like tantalum (Ta) and tantalum nitride (TaN) are currently deposited in the damascene trench/via features by physical vapor deposition (PVD) to contain Cu interconnects to prevent catastrophic contamination caused by copper diffusion. An additional Cu seed layer is deposited on Ta/TaN to ensure the success of bottom up Cu electrofill process. Recent advances in PVD technology has extended the applicability of Ta/TaN barrier down to the 90 nm node and likely into 65 nm as well. However, Cu-seed/Ta/TaN tri-layer configuration will encounter scaling difficulties in the case of 45 nm node. The thickness of a functional diffusion barrier is limited to 5 nm or less at the 45 nm node. Hence, a single layer Cu plateable diffusion barrier is desirable to optimize the overall integration by eliminating Cu seed layer for the advanced 65-45 nm nodes.
Ruthenium (Ru) is a promising metal for Cu diffusion barrier which affords direct Cu electroplating without the need of an additional Cu seed layer. Ru is an air stable transition metal with high melting point (2310° C.) and is nearly twice as thermally and electrically conductive (7.6 μΩ.cm) as Ta. Similar to Ta, Ru shows negligible solid solubility with Cu even at 900° C.
Typical ruthenium slurry in required to remove the barrier material without adversely impacting the dielectric or electrical properties of interconnect structure. Polishing compositions that have been developed for Ru and other noble metals typically contain strong oxidizing agents and working at a low pH. Cu tends to oxidize very rapidly in these polishing compositions. Additionally, because of the difference in standard reduction potentials of Ru and Cu, Cu suffers from galvanic attack by Ru in the presence of conventional Ru polishing compositions. Galvanic corrosion leads to etching of Cu lines and a resulting degradation of circuit performance. Further, the wide difference in chemical reactivity of Cu and Ru in conventional polishing compositions results in widely differing rates of removal of substrates containing both the metals, which can result in over-polishing of Cu. In view of the above, there exists a need to provide ruthenium slurry that possesses a high removal rate of ruthenium and controlled removal of dielectric and copper interconnects.
A need remains for polishing slurry that will provide desirable planarization efficiency, uniformity and removal rate while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during chemical mechanical planarization. Improved polishing systems are particularly needed for polishing noble metal containing substrates, since noble metals are known to be chemically stable and mechanically hard materials. The present invention seeks to provide such a chemical mechanical polishing system for substrates comprising Ru.